title: RRR-alpha-tocopherol can be substituted for by Trolox in determination of kinetic parameters of LDL oxidizability by copper.
abstract: LDL resistance to oxidation is characterized by the lag time that precedes the rapid generation of conjugated dienes in copper-induced oxidation. Lag time (y) is described by the equation y = kx + a, where k is the efficacy constant of alpha-tocopherol (alpha-TOH), x the alpha-TOH content of LDL, and a the alpha-TOH-independent variable, all of which show considerable between-subject variability. To answer the question of whether loading of LDL with Trolox can substitute for the more timeconsuming loading with RRR-alpha-TOH in large scale studies focusing on determination of k and a values, LDL from 15 healthy subjects was loaded in vitro with 0-50 mol Trolox/mol LDL or 0-250 mM RRR-alpha-TOH. In addition, five of these subjects were supplemented in vivo with 800-1200 IU/d RRR-alpha-TOH for 17 days and k and a were determined. The ratios k(Trolox):k(alpha-TOH) and alpha(Trolox):a(alpha-TOH) were calculated. The k(Trolox) was only slightly higher than k(alpha-TOH), in contrast to alpha(Trolox), which was almost twice as high as a(alpha-TOH), indicating that, in the case of Trolox, a includes the contribution of alpha-TOH to the lag time. In the case of alpha-TOH, a includes only the additional antioxidants that occur naturally in LDL. The ratios k(Trolox):k(alpha-TOH) and alpha(Trolox):a(alpha-TOH) showed little variability, both between subjects and between in vitro and in vivo experiments. A close correlation was found between k(alpha-TOH) and a(alpha0TOH), calculated using this ratio, and k(alpha-TOH) and a(alpha-TOH), obtained in our experiments. We conclude that from this ratio, k(alpha-TOH) and a(alpha-TOH) can be reliably calculated when k(Trolox) and a(Trolox) are determined experimentally, thus allowing us to obtain k and a values in a more convenient way.
authors.affiliation: Institute of Biochemistry, Karl-Franzens University of Graz, Austria.
authors.forename: A R
authors.initials: AR
authors.lastname: Bergmann
authors.forename: P
authors.initials: P
authors.lastname: Ramos
authors.forename: H
authors.initials: H
authors.lastname: Esterbauer
authors.forename: B M
authors.initials: BM
authors.lastname: Winklhofer-Roob
mesh_terms: D000328:Adult; D000975:Antioxidants / Q000378:metabolism; D002839:Chromans / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000032:analysis* / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D012044:Regression Analysis; D013053:Spectrophotometry; D014810:Vitamin E / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D002839:Chromans; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D014810:Vitamin E; D003300:Copper; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid